Until there is a cause of death from a thorough autopsy, I think it's too early to say whether this is suspicious or not. I can't believe you are being upvoted for saying this.
"Hacker dies days before he was to reveal how to remotely kill pacemaker patients"
http://rt.com/usa/hacker-pacemaker-barnaby-jack-639/
Edit: It seems very relevant to keep in mind that this is not the first time someone (or even Jack in particular) had demoed remote kill switch functionality for human beings. http://www.bloomberg.com/news/2012-02-29/mcafee-hacker-says-...
Perhaps consider that many posters and readers here knew him in person.
Because he sounds to me like a guy who really loved busting people's assumptions, in your face, and without apology.
Even with that in mind: technology is probably sufficiently advanced today to be able to not leave any traces, if the budget is there.
Plus, don't forget that Hastings [1] was cremated without his family asking for it (there is always one way or another to make traces disappear).
[1] http://en.wikipedia.org/wiki/Michael_Hastings_%28journalist%...
(Note: concern, I am not claiming there was some conspiracy theory)